The present invention relates to an apparatus for the production of concrete pipe. In particular, the invention is concerned with an improved packerhead assembly configuration, which is particularly useful in the manufacture of concrete pipes with which highly fluid concrete mixes are used.
Manufacturers of concrete pipe have for many years used machines which employ apparatus known as "packerheads" or "packerhead assemblies". In such machines, a large, inverted U-shaped main frame is used in connection with a drive-shaft to which the packerhead is connected. The packerhead assembly is lowered into a form, and the packerhead is placed at the bottom of the form. As concrete is placed around the inside periphery of the form, the packerhead is raised. Rotational movement of the components of the packerhead cause the concrete to be packed and smoothed as the packerhead is raised.
In U.S. Pat. No. 4,540,539, which is assigned to the assignee of this invention and which is incorporated herein by reference, the operation of a typical packerhead assembly is shown and described. In addition, U.S. Pat. No. 4,540,539 describes a bi-directional packerhead in which the roller assembly and the longbottom assembly are rotated in opposite directions. A typical packerhead assembly includes a longbottom and a roller assembly, the longbottom being the lowermost component of the packerhead assembly. In most cases, a very dry mix of concrete is used in connection with packerhead assemblies. However, in some cases, wetter concrete mixtures provide a higher strength concrete and a better bond between the concrete material and steel reinforcing framework around which the concrete is placed. Unfortunately, higher water content significantly increases the likelihood that concrete will flow or otherwise deform after the packerhead assembly has been raised above a particular level. Increasing demand for higher strength concrete pipe has made traditionally designed packerhead assemblies less effective. The consequences of using wetter concretes are particularly noticeable in the case of pipes having large wall thickness. There is a tendency for the concrete in thicker walls to flow downwardly and inwardly after a longbottom has been raised from its lowest position. Attempts have been made to increase the length of longbottoms. Longbottoms having axial lengths of 10 inches have been used in conjunction with roller assemblies with axial lengths of 10 inches. However, such arrangements are quite expensive in that they require the use of specially designed equipment and components.
Another difficulty encountered when using concrete mixes which have higher than normal fluidity or water content is the tendency for such mixes to infiltrate the packerhead assembly. Such infiltration of concrete material causes increased wear on moving components of the packerhead assembly, and results in splatter of the infiltrating concrete as it comes into contact with the rotating longbottom.
Therefore, it is an object of the present invention to provide a packerhead assembly which is designed for use with concrete mixes having relatively high fluidity.
Another object of the present invention is to provide a packerhead assembly in which standard roller assembly and longbottom assembly components can be used.
Yet another object of the present invention is to provide a packerhead assembly in which wear on rotating parts is reduced.
Yet another object of the present invention is to provide a specially designed longbottom assembly which is usable with relatively wet concrete.
Still another object of the present invention is to provide an apparatus particularly useful for making concrete pipes with thick walls.
These and other objects of the present invention are achieved with the packerhead assembly which includes a long-bottom assembly and a rollerhead assembly, such assemblies being rotatable in opposite directions. The longbottom assembly is comprised of a longbottom support plate and a long-bottom cylinder. The longbottom cylinder extends a substantial distance below the longbottom plate, and is preferably comprised of two 6-inch segments. The segments are those which are typically used with a standard packerhead assembly. However, the lower of the two longbottom segments is inverted, and mounted adjacent to an upper identical segment. The longbottom segments are mounted to a mounting flange, which is integral with the longbottom plate. The longbottom flange is equipped with a removable wear band attached to the upper surface of the mounting flange to limit the ingress of concrete material to the area around the rollerhead assembly. The wear band extends upwardly from the uppermost level of the long-bottom to a position approximately 1/8-inch from the lowermost portion of the rollers of the roller assembly.